Show "Last checked" always in Updates page
While looking into #2513 (closed), I noticed that update metadata is not always refreshed as per the schedule mentioned in #2513 (comment 2080278). Looking into the code, there are a lot of conditions in check_updates (GsUpdateMonitor *monitor)
where we return without refreshing metadata. In such cases, it would be useful to show "Last checked"
time in Updates
page.
Also, these conditions should be properly logged via g_debug ()
for debugging.